I can't find a 'getting started' section - particularly for those not familiar with any of this.

I have installed ampps on my windows 7 machine. I understand what an add on domain is and a parked domain is in relation to my accounts with godaddy and hostgator. But the domains I add are on my machine, so how do I know why I would want a parked domain or a addon domain?

In Parked Domain, you have two domains mysite.com and my-other-site.com.
mysite.com is the domain of your website and you want to add my-other-site.com.
You want them both to go to the same place. In other words, when someone types either www.mysite.com or www.my-other-site.com they will go to the same page(s) on your website.

While in Add-On Domains, you have two domains mysite.com and my-other-site.com. You want the two domains to be totally separate/independent websites.

Regarding AMPPS, you can refer our wiki i.e http://www.ampps.com/wiki and for Apache you can refer their Official Website/Manual.